Furnace



July 20, 1937 E. G. BAILEY ET AL 2,087,800

FURNACE Filed Nov. 16, 1934 I 3 Sheets-Sheet 1 Fig- I 20 EINVIIEN gi /eI V O O O O 51 MO 0 E g]: MfHardg npve B Howard J. Kefh AT ORNEY July20, 1937 G, BNLEY ET AL 2,087,800

FURNACE Filed Nov. 16, 1954 s Sheets-Sheet 2 IN VENTOR.S E'r n G. BaileyRa ph M; Hardgro/g Hoya'raj Kerr Aho NEY July 20, 1937 E. G. BAILEY ETAL 2,087,300

FURNACE Filed Nov. 16, 1954 '5 Sheets-Sheet 5 Fly. 4

INYENTORS Ervm G. Baildy e Ralph M. Har grave Howa JKerr E A fioRl lEYPatented July 20, 1937 UNITED STATES PATENT OFFICE FURNACE Ervin G.Bailey, Easton, Pa., Ralph M. Hardgrove and Howard J. Kerr, Westfield,N. J., assignors to The Babcock & Wilcox Company, Newark, N. J., acorporation of New Jersey Application November 16, 1934, Serial No.753,272

18 Claims.

means is provided for controlling the mean temperature of the furnaceand for disposing of the ash resulting from the combustion of aslagforming fuel in suspension in a furnace chamber.

A further object of the invention is to provide an improved method ofburning a slag-forming fuel in a furnace chamber.

These and other objects are elfected by our invention, as will beapparent from an examination of the following description and claims,taken in connection with the accompanying drawings, in which:

Fig. 1 is a vertical sectional view of a boiler furnace constructed inaccordance with the present invention;

Fig. 2 is a transverse section taken on the line 2-2 of Fig. 1 andillustrating one preferred arrangement of tubes which form the perviouswater-cooled screen through which the furnace gases flow;

Fig. 3 is a view similar to Fig. 1 illustrating a slightly modifiedfurnace arrangement;

Fig. 4 is a view also similar to Fig. 1 illustrating a furthermodification of our invention;

Fig. 5 is a fragmentary section of the front wall of the furnace and istaken on the line 5-5 of Fig. 1; and

Fig. 6 is a fragmentary section of the rear wall taken on the line 66 ofFig. 1.

According to one embodiment of our invention, we provide a plurality offurnace walls which define a chamber for the combustion of a slagformingfuel; the slag-forming fuel being introduced downwardly and along oneside of the a chamber and an outlet being provided in the upper portionof the chamber and at the side opposite the point of introduction of thefuel, whereby the stream of burning fuel and gaseous products ofcombustion follows a U-shaped flow path with the bottom of the U alongthebottom of the chamber and the legs at opposite sides of the chamber.

That portion of the bottom of the combustion chamber which is at thesideadjacent the fuel inlet is formed to collect molten ash or slag in apool, and that portion of the bottom which is adjacent the other 'or gasoutlet side of the chamber is formed to collect chilled-or dry ashparticles. Molten ash is released in the downwardly moving stream bycombustion at a, sufiiciently 'high temperature and the change indirection of flow of the stream of burning fuel from downward tosidewise results in the separation out. of the stream of the molten ash,which collects on that portion of the bottom of the furnace constructedto receive it.

A pervious water-cooled screen is disposed between the two portions ofthe bottom and across the flow path of the burning fuel stream, andfunctions to catch at least a portion of the molten ash in the streamwhich has not been previously separated out by the change of directionof flow,

and causes such ash to gravitate to that portion of the bottom which-isformed to receive the molten ash. The screen also functions to mix theremaining combustible matter and air in the stream and thereby promotesthe combustion of such combustible matter. to retard or prevent thetransmission of radiant heat from the hotter side of the chamberadjacent the fuel inlet to the colder side of the chamber adjacent thegas outlet. The amount of heat released by combustion in relation tocold wall heat receiving surface is greater in the former part of thechamber than in the latter, so the mean temperature of the former ishigher, and the temperature of both parts of the chamber is differentthan if the screen were not provided, especially as the load changes.

Referring now in detail to the construction illustrated and particularlyto Figs. 1 and 2, the reference number 9 indicates, in its entirety, aboiler furnace constructed in accordance with the present invention. Thefurnace 9 comprises a combustion chamber l0 defined by front and rearwalls I I and. I2 respectively, side walls 3 (only one side wall beingshown), and a botto n,

' l4 divided into a portion l5 constructed to retain a pool of moltenash or slag and a portion l6 constructed to collect and remove chilledor dry ash particles.

A roof or arch portion I1 is provided in the upper portion of thecombustion chamber l0 and at one side thereof. Burners l8 are providedfor introducing through the roof portion, a stream of slag-forming fueland air more or less vertically downward into the combustion chamber. Ifdesired, the fuel used may be coal which is pulverized to a degree offineness sufficient to permit its being burned in suspension in thecombustion chamber.

The combustion chamber [0 is provided at the side opposite the roofportion H with an outlet IQ for the furnace gases, a steam boiler 20,here shown to be of the horizontally inclined water tube type beingdisposed across the outlet and The screen also serves absorbing heatderived from the combustion of the fuel in the combustion chamber.Preferably the front and rear walls II and I2,

the side walls i3, and the roof portion I! are of the water cooled typeand are composed of spaced tubes 2| with closure members for the spaces.While any of the conventional types of closure members or coverings maybe used for the tubes without departing from certain aspects of ourinvention, we have shown. the spaces between the tubes as closed and thetubes covered by heat-resistant blocks 22 secured to the tubes andproviding the interior surface of the combustion chamber In. Oppositethe burners l8 the heatresistant blocks 22 are omitted to permit theintroduction of the fuel and air into the chamber through the spacesbetween tubes.

The tubes 2| forming the walls of the furnace are connected into theboiler circulation system so as to assure circulation of water throughthe tubes for cooling the latter and so that the heat from thecombustion chamber may be utilized in making steam. The front wall ii isprovided with an inlet header 23 and an outlet header 24 connectedrespectively to the ends of the tubes forming the wall. Similarly, therear wall is provided with inlet and outlet headers 25 and 26respectively, the side wall with inlet headers 21 and outlet headers 28and 29, and the roof portion with inlet and outlet headers 30 and 3|respectively. The inlet headers 25, 21 and 30 may be each connected bydowncomers 32 with the water space of the boiler. The inlet header 23 isconnected to the upper end of a row of horizontally-inclined spacedtubes 33 embedded in the portion l5 of the bottom. The lower ends of thetubes 33 are connected to a header 34 to which downcomers 35 are in turnconnected. The outlet headers 24, 26, 28, 29 and 3| are connected byupcomers or risers 36 with the steam and water drum of the boiler. Inorder to promote local circulation in the rows of wall tubes,recirculating tubes 31 may be provided to connect any or all of thepairs of inlet and outlet headers.

As previously stated, the portion i5 of the furnace bottom isconstructed to provide for the collection thereon of the molten ash orslag and for the removal of the slag from the furnace. In Fig. 1 theportion i5 is illustrated as being water cooled and comprising the tubes33 with suitable means for closing the spaces between the tubes, forexample, heat-resistant blocks 38 secured to the tubes. The portion |5may be suitably supported by structural members 39. We prefer tomaintain a pool of molten ash or slag on the portion l5 of the furnacefloor, as indicated at 40 in Fi 1.

During furnace operation, the heat from the burning fuel willmaintain atleast the surface of the slag pool in a fluid or molten condition byreason of the large amount of heat released by combustion per unit areaof cold absorbing wall of the space above they pool, and at lightloadsthe combustion may be wholly completed in this 1 space. .However, theportion of the slag in the ber bottom is constructed to provide for thecolbottom which contacts with the heat-resistant blocks may becomechilled, thereby providing a solidified layer of slag which aidsinprotecting the portion l5 of the floor from the heat of the furnace andfrom the destructive action of. the molten slag above. We have indicatedat 4| a slag-tap opening through which the slag may be eitherperiodically or-continuously tapped.

As stated, the portion l6 .of thefurnace chamlection and removal ofchilled or dry ash or slag particles and this chilling is the resu t ofa s i ciently low average temperature resulting from the relativelylarge amount of cold heat absorbingwall surface of this part of thechamber in which the heat released is less than in the other and atlight loads there may be little combus tion here. In the embodiment ofour invention, illustrated in Fig. 1, we have shown the portion l6-ascomprising a hopper 42 disposed beneath an opening 43, ,the latter beingdefined by the lower end of the water-cooled rear wall l2, the lowerends of the side walls l3, and a water cooled wall 44 adjacent the sideof the portion |5 supporting the slag pool. The dry or chi led ash maybe removed from the hopper 40 in any suitable manner, for example,through a door controlled opening 45.

A short partition wall 46 extends downwardly and diagonally from theupper portion of the combustion chamber and in conjunction with the sidewalls l3, the front wall H and rear wall I2, defines a downflow passage41 and an up-flow passage 48 connected at their lower ends to pr" vide aU-shaped flow path for the burningfuel and gaseous products ofcombustion.

The partition wall 46 is composed of spaced water tubes 49 with meansclosing the spaces between tubes, for example, heat-resistant blocks 50secured to each side of the tubes. The tubes 49 extend upwardly from thepartition wall 46 and are connected at their upper ends to the outletheader 3| previously described. We have shown the portion of the tubes49 above the wall 46 as not being provided with the heat-resistantblocks 50.

The tubes 43 extend downwardly from the partition wall 46 and arearranged in groups 5| and 52, which groups may be arranged as indicatedin Fig. 2 to provide a pervious water-cooled screen 53 extending acrossthe U-shaped flow path of the burning stream. The lower ends of thetubes 49 may be covered by heat-resistant blocks 54 and thus form thewater cooled wall 44 which was previously described as defining in partthe opening 43 and hopper 42. An inlet header 55 is connected to thelower ends of the tubes 49, and a downcomer 56 is connected to theheader 55 to supply the latter with water from the water space of theboiler.

It is to be observed that while we have shown in Fig. 2 a particularform and position of screen, our invention in its broader aspects is notso limited, for other structures may be used without departing from itsintended scope. For example, screen structures like those shown in ourPatents Nos. 2,002,463 and 2,002,464, may be used if the properconditions exist; or, if desired, a structure like thatshown in theco-pending application of Rolfe Shellenberger, Ser. No. 750,342, filedDec. 27, 1934,; may be used. Furthermore, with any form of screen, thedivision of the chamber and other factors are to be such that themeantem perature of the down-flow passage shall be normally above slagfusion temperature and that of the up-flow passage 'normally below ashfusion temperature. v

The diagonally disposed partition wall 46 and I an inclined lowerportion 51 of the rear wall l2,

in conjunctionwith the front and side walls and|3 respectively, and theremaining portions of the rearwall I2,,provide a downward div'ergence,to the down-flow passage 41 and an upward divergence to the up -fiowpassage 48. The purmoves downwardly along its flow path and thetemperature thereof becomes higher and to assist in the combustion ofenough of the fuel to make the mean temperature of the space higher thanash fusion temperature. The purpose of the divergence in the up-fiowpassage is to equalize the distribution of the gases across the outletand to effect a reduction in fiow velocity of the stream after it passesthrough the screen 53 so as to permit the dry ash particles to settleout of the stream into the hopper 42. The flow path of the burningstream is changed in direction and is somewhat restricted by the screen53, as a result of which the velocity of the stream is increased at thispoint, the purpose of which will presently appear.

The fuel is ignited as it enters the combustion chamber under conditionsthat cause it to burn rapidly. Before the fuel reaches the bottom,combustion has proceeded far enough to have released a large portion ofthe ash which is separated out of the stream in a molten form due to thehigh temperature of this space. The separated molten ash collccts on theportion l5 of the bottom due to the change in direction of flow of thestream. Such ash or slag as has not been previously separated passesthrough the screen which serves to catch at least a substantial portionof the slag, the collected slag dropping from or running down the screeninto the pool. Combustion conditions in the down-flow passage inrelation to the cooling of its walls are such as to not only keep themean temperature higher than the ash fusion point, but to be actuallyhottest near the pool of molten slag. The ash in the fuel is liberatedin the down-flow passage wholly or substantially becauseof thesubstantial completion of combustion of the fuel therein and as stated,is separated out of the stream due to the change in direction of fiow.of the stream and also to the slag catching func-- tion of the screen53.

In addition to the slag catching function just described, the screen 53serves to mix theconstituents of the stream passing therethrough,

and thereby promotes the completion of combustion of the combustiblematter therein. As stated previously, the mixing function of the screenis aided by the fact that the fiow area through.

tributing to the chilling or solidifying of the molten ash carried overfrom the down-flow passage to the cooler chamber beyond so that such ashmay settle out of the stream in the up-flow passage;

A further function of the screen is to reduce the transmission ofradiant heat from the'relatively higher temperature space'ofthe'downfiow passage 41 to the cooler space of the up-flow passage 48,thereby aiding insustaining the desired temperature difference. Thechilling of the ash in the up-fiow passage tends to reduce or preventthe harmful deposition of slag on the boiler tubes. N

As the up-fiow passage 48 diverges upwardly, and the passage is definedby Water-cooled walls of suificient area, and as a relatively smallamount of heat is released in the passage, the temperature of the streamis lowered to a degree s'ufficient to promote the effective chilling ofthe molten ash or slag remaining in the stream; the reduction invelocity of the stream serving to promote the settlingout of the streamof the chilled ash particles into the hopper 42.

From the above, it will be apparent that the temperature within thedown-flow passage 47 is maintained relatively higher than thetemperature within the up-fiow' passage 48. As stated previously, onepurpose of the difference in temperature between the two passages is toefiect early ignition and combustion of the fuel in the down-flowpassage so that the ash may be liberated and separated out'of the streamand collected in the pool, and to effect a cooling of the stream in theup-flow passage so that remaining ash may be chilled and separated outin the up-fiow passage. Atlight loads all of the combustion may becompleted in the down-flow passage and the pool kept molten when itmight freeze if the screen were removed because the flame gases couldthen radiate to a larger area, that of the whole furnace boundary.

It is within the scope of the present invention to provide a furnacewall structure defining the passages 41 and 48 which aids in pro vidingthe desired high temperature condition in the passage 41 foraccelerating the combusi-' tion process therein and the desiredrelatively low temperature condition inthe passage 48 for aid ng in thechilling of the remaining ash in the stream. This may be accomplished ina num-- ber of ways, for example, the blocks 22 covering the tubes 2|and the blocks 50 covering the tubes 49 which provide the wall structurefor the passage 41 may be formed in whole or in part with a ceramicrefractory material and the blocks 22 .and 50 defining the passage 48may be formed of a metallic refractory. Fig. 5 is a fragmentary sectionthrough the front wall H and illustrates the blocks as being formed ofcast metal with a ceramic refractory facing. Fig. 6 is a fragmentarysection through the rear wall l2 and illustrates a bare metal refractoryblock. .The ceramic material has relatively higher insulatingqualitiesthan the bare metal refractory and slag-tap bottom l5a forthe down-flowpassage 41a. The bottom I5o is composed of layers BI' hence a highertemperature will be had in the of suitable refractory, for example,dolomita,

supported by a plate structure 62 which is in turn supported bystructural members 63. The portion 16a of the furnace bottom which isconstructed to collect and remove the chilled slag from the passage 48ais also slightly different, in that we .have shown a horizontallymovableash gate ,64. v

The construction shown. in Fig.' 3 occupies a smaller cross-sectionalarea of the boiler room than the structure of Fig. '1. Because the rearwall I2a is disposed vertically instead of having a bend in the lowerend like Fig. 1, the front walllla. may be arranged more nearly beneaththeboiler and the same furnace chamber area obtained. A further featureof the structure shown in Fig; 3 is that the wall tube arrangement issomewhat simplified and there are fewer bends in the tubes, viz: thetubes 2la forming the rear wall l2a are straight; the front wall Ha andthe roof portion l'la are formed of the same tubes, thereby reducing thenumber of headers required; and the tubes forming the partition 46a andthe screen 53a extend diagonally downward from the front of the boilerand thereby require fewer bends.

The embodiment shown in Fig. 4 is also similar in structure andoperation to that of Fig. 1. The principal distinguishing feature ofFig. 4 is the relatively high furnace and the vertical arrangement ofthe partition wall D. The sides of the tubes 4% forming the partitionwall 46b which are adjacent the up-fiow passage 481) are bare, whichaids in the cooling of the stream in the up-fiow passage. The rear wallI2!) is formed of straight tubes as was the case in Fig. 3. In Fig. 4,the down-flow passage 41b and the up-fiow passage 48b do not increase incrosssectional area in the direction of stream fiow. The up-flow passageis relatively large,'-and the hopper 42b for chilled ash is also large.The walls of the hopper 42b are formed of water tubes 10 and refractoryblocks ll secured to the tubes.

From the above description, it will be apparent that in each of themodifications we have provided a furnace which is of improvedconstruction and arrangement of parts. In each of the structures thedivision of the furnace chamber into a relatively hot down-flow passageand a relatively cool up-fiow passage with the molten ash collection atthe bottom of the down-fiow passage and the dry ash removal at thebottom of the up-flow passage in conjunction with the screen, provides afurnace which operates effectively and efficiently and a furnace havingan improved means for disposing of the ash.

While we have shown our invention in three forms. it will be obvious tothose skilled in the art that it is 'not so limited but is susceptibleof various other changes and modifications without departing from thespirit thereof, and we desire, therefore,, that only such limitationsshall be placed thereupon as are imposed by the prior art or as arespecifically set forth in the appended claims.

We claim:

1. In a furnace for burning a slag-forming fuel, the combination ofmeans defining a combustion chamber including a floor portion, one partof which is constructed to support and provide for the removal of moltenslag and another part of whichis constructed to collect chilled slagparticles; means providing for the introduction of a stream ofslag-forming fuel with air for supporting combustion chamber; meansproviding for the movement of the stream first over the part of thefloor supporting the molten slag and then over the part where thechilled slag is collected; and means for chilling the slag in the streamafter the latter passes over the part supporting the molten slag.

2. A method of operating a furnace which comprises introducing into thefurnace chamber a stream of slag-forming fuel and air; effectingmovement'of such stream in a predetermined path through the furnacechamber; igniting and effecting combustion of the fuel while insuspension; removing from the stream a portion of the ash resulting fromcombustion while the ash is in a molten form and collecting the moltenash in a pool in the lower portion of the furnace; chilling theremaining ash in the stream; and

thereof into the combustion collecting the chilled ash in the lowerportion of the furnace and at points spaced from the slag pool.

3. In a furnace for burning slag-forming fuel, the combination of meansdefining a combustion chamber; means delineating a down-flow and anup-fiow passage in the combustion chamber intercommunicating at theirlower ends; means providing for the introduction of a stream ofslagforming fuel and air for supporting the combustion thereof into theupper end of the down-fiow passage; means at the lower end of thedownfiow passage providing for the collection of molten slag resultingfrom combustion; means at the lower end of the up-fiow passage providingfor the separate collection and removal of chilled slag particles; andmeans providing a cooling surface over which the stream fiows in passingfrom the down-flow to the up-fiow passage so as to lower the temperatureof the stream and chill the remaining slag particles therein.

' 4. In a furnace for burning a slag-forming fuel, the combination ofmeans defining a combustion chamber; means delineating a down-flow andan up-fiow passage in the combustion chamber intercommunicating at theirlower ends; means providing for the introduction of a stream ofslagforming fuel and air for supporting the combustion thereof into theupper end of the downfiow passage; means at the lower end of thedown-flow passage providing for the collection of molten slag resultingfrom combustion; means at the lower end of the up-flow passage providingfor the collection and removal of chilled slag particles; saiddelineating means including a row of spaced water cooled surfacesthrough which the stream passes in flowing from the down-flow passage tothe up-fiow passage; the row of tubes extending downwardly to that edgeof the molten slag collecting means which is adjacent the lower end ofthe up-fiow passage.

5. In a furnace for burning a slag-forming fuel, the combination ofmeans defining a combustion chamber; means delineating a down-flow andan up-fiow passage in the combustion chamber intercommunicating at theirlower ends; means providing for the introduction of a stream ofslag-forming fuel and air for supporting the combustion thereof into theupper end of the down-flow passage; means at the lower end of thedown-flow passage providing for the collection of molten slag resultingfrom combustion; means at the lower end of the up-fiow passage providingfor the collection and removal of chilled slag particles; thedelineating means including a water-cooled screen comprising a row ofspaced water-cooled tubes extending across the fiow path of the streamand to the lower portion of the furnace and between the molten slagcollecting means and the chilled slag collecting means.

6. In a furnace for burning slag-forming fuel, the combination of meansdefining a combustion chamber; means delineating a down-flow and anup-flow passage in the combustion chamber intercommunicating at theirlower ends; means providing for the introduction of a stream ofslagforming fuel and air for supporting the combustion thereof into theupper end of the downfiow-passage; means at the lower end of thedown-flow passage providing for the collection of molten slag resultingfrom combustion; means at the lower end of the up-fiow passage providingfor the collection and removal of chilled slag particles; thedelineating means including a water-cooled screen comprising a pluralityof rows of spaced water-cooled tubes extending across the flow path 'ofthe stream and to the lower portion of the furnace chamber and bebeingarranged in staggered relation with respect to the tubes of an adjacentrow so as to provide a multitude. of tortuous paths for the streamflowing through the screen.

7. In a furnace for burning a slag-forming fuel, the combination ofmeans defining a combustion chamber including upright side walls; apartition wall extending downwardly from the upper portion of thechamber and terminating short of the lower portion of the chamber todivide the latter into first and second substantially vertical passagesconnected at their lower ends to provide a U-shaped flow path for thefuel undergoing combustion; means for cooling the side wall structure ofthe furnace chamber; means providing for the introduction of a stream ofslag-forming fuel and air for supporting combustion thereof into theupper end of the first passage; means at the lower end of the firstpassage providing for the collection of molten slag resulting from thecombustion of the fuel; means providing a posi-- tively cooled screenthrough which the stream flows in passing from the first to the secondpassage so as to lower the temperature of the stream and chill theremaining slag particles; and means in the lower portion of the secondpassage providing for the separate collection and removal of slagchilled while passing through said screen and by the action of thecooled walls of the second passage.

8. In a furnace for the combustion of a slagforming fuel, thecombination of wall means dedownflow passage and having its surfaceconstructed to maintain fining a Ushaped passage for the flow of fuelundergoing combustion; the construction and arrangement of thepassage-defining wall means being such that the legs of the U extendupwardly and the'base of the U extends along the bottom of the furnace;means for introducing a slagforming fuel and air into the upper end ofone of the legs of the U-shaped passage; an outlet for the furnace gasesat the upper end of the other leg of the U-shaped passage; means beneathsaid one leg and a portion of the base of the U-shaped passage forcollecting molten slag in a pool;

.Ineans beyond the last mentioned means, considered in the direction offuel travel, for chilling fuel comprising front, rear and side wallsdefining a combustion chamber, means extending downwardly across thefurnace intermediate the ends thereof for defining a front downflowpassage and a rear up-flow passage communicating at their lower ends,means for introductingslagforming fuel into the upper end of and burningthe same in suspension in said downflow passage, heat absorbing meanslining the walls of said heat absorbing a normal mean temperature in.said downflow passage higher than the ash fusion temperature of the fuelburned therein, heat absorbing means lining the walls of said up-fiowpassage and having its heat absorbing surface constructed to maintain anormal mean temperature in said upfiow passage lower than the ash fusiontemperature of the fuel burned in said downflow passage, the portion ofsaid furnace bottom directly below said downflow passage of said furnacebottom directly below said upfiow passage being constructed as a hopperextending below the level of said floor.

10. A furnace for the burning of slag-forming fuel comprising front,rear and side walls defining a combustion chamber, an arch extendingover the front upper portion of said combustion chamber, a heating gasoutlet between the rear end of said arch and said rear wall, meansincluding a group of water screen tubes extending downwardly across thefurnace from said arch to the combustion chamber bottom intermediate theends thereof for defining a front downflow passage and arear up-flowpassage communicating at their lower ends, means in said arch forintroducing slag-forming fuel into the upper end of and burning the samein suspension in said downflow passage, fluid heating surface lin-' ingthe walls of said downflow passage and con structed to maintain a normalmean temperature in said downflow passage higher than the ash fusiontemperature of the fuel burned therein, fluid heating surface lining thewalls of said upflow passage and constructed to maintain a normal meantemperature in said upfiow passage lower than the ash fusion temperatureof the fuel burned in said downflow passage, the portion of said furnacebottom below said downflow passage being constructed to receive slagparticles in a molten condition, andthe portion of said furnace bottombelow said upfiow passage being constructed to receive condition. l

11. A furnace for burning finely divided solid fuel comprisingvertically disposed front, rear and side walls defining a furnacechamber, means forming a transverse baffle extending downwardly andterminating above the bottom of said furnace chamber to separate a frontdownflow passage and a rear upfiow passage communicating at their lowerends, means for burning finely divided solid fuel in suspension in saiddownflow passage, means arranged to form a pervious fluid cooled screenbetween the lower end of said baflie and an intermediate portion of thefurnace bottom, a floor forming the furnace bottom at the front sideofsaid screen, and a hopper forming the furnace bottom at the rear side ofsaid screen. 12. A furnace for burning finely divided solid fuelcomprising vertically disposed front, rear and side walls defining afurnace chamber, an' arch extending .rearwardly from said front wallover the front portion of said furnace chamber, means forming atransverse baflle extending downwardly from said arch. and terminatingabove the bottom of said furnace chamber to separate a front downflowpassage and a rear upfiow passage communicating at their lower ends,means in said arch for introducing finely divided solid fuel into theupper end of and burning the same in suspension in said downflowpassage, water tubes arranged to form a pervious fluid cooled screenbetween the lower end of said baflle and an intermediate portion of thefurnace bottom, a forwardly inclined floor forming the furnace bottom atthe front side of said screen, a row of inclined water tubes arrangedalong and cooling said floor, and a hopper forming the furnace bottom atthe rear side of said screen and arranged to directly receive ashparticles separated in said upfiow passage.

ash particles in a dry 13. A furnace for burning finely divided solidfuel comprising vertically disposed front, rear and side walls defininga furnace chamber, means forming a transverse baflle extendingdownwardly and terminating above the bottom of said furnace chamber toseparate a front downfiow passage and a rear upfiow passagecommunicating at their lower ends, means for burning finely dividedsolid fuel in suspension in said downfiow passage, heat absorbingsurface lining the sides of said downfiow passage and constructed tomaintain a normal mean temperature therein higher than the fuel ashfusion temperature, heat absorbing surface lining the sides of saidupfiow passage and constructed to maintain a normal mean temperaturetherein lower than the fuel ash fusion temperature, and means arrangedto form a pervious fluid cooled screen between the lower end of saidbaflle and an intermediate portion of the furnace bottom.

14. A furnace for burning finely divided solid fuel comprisingvertically disposed front, rear and side walls defining a furnacechamber, an arch extending rearwardly from said'front wall over thefront portion of said furnace chamber, means forming a transverse bafileextending downwardly from said arch and terminating above the bottom ofsaid furnace chamber to separate a front downfiow passage and a rearupfiow passage communicating at their lower ends, means for burningfinely divided solid fuel in suspension in said downfiow passage, heatabsorbing surface lining the sides of said downfiow passage andconstructed to maintain a normal mean temperature therein higher thanthe fuel ash fusion temperature, heat absorbing surface lining the sidesof said upfiow passage and constructed to maintain a normal meantemperature therein lower than the fuel ash fusion temperature, a floorforming the furnace bottom below said downfiow passage and constructedto receive ash particlesin a molten condition, and a hopper forming thefurnace bottom below said upfiow passage and constructed to receive ashparticles in a dry condition.

15. A furnace for burning finely divided solid fuel comprisingvertically disposed front, rear and side walls defining a furnacechamber, means forming a transverse bafile extending downwardly andterminating above the bottom of said furnace chamber to separate a frontdownfiow passage and a rear upfiow passage communicating at their lowerends, means for burning finely divided solid fuel in suspension in saiddownfiow passage, heat absorbing surface lining the sides of saiddownfiow passage and constructed to maintain a normal mean temperaturetherein higher than the fuel ash fusion temperature, heat absorbingsurface lining the sides of said upfiow passage and constructed tomaintain a normal mean temperature therein lower than the fuel ashfusion temperature, and means arranged to form a pervious fluid cooledscreen between the lower end of said bafile and an intermediate portionof the furnace bottom, said furnace bottom being constructed at thefront side of said screen to receive ash particles in a molten conditionfrom said downfiow passage and at the rear side of said screen toreceive ash particles in a dry condition from said upfiow passage.

16. A furnace for burning finely divided solid fuel comprisingvertically disposed front, rear and side walls defining a furnacechamber, an arch whereby ash separating extending rearwardly from saidfront wall'over the front portion of said furnace chamber, means forminga transverse baffle extending downwardly from said arch and terminatingabove the bottom of said furnace chamber to separate a front downfiowpassage and a rear upfiow passage communicating at their lower ends,means for burning finely divided solid fuel in suspension in saiddownfiow passage, heat absorbing surface lining the sides of saiddownfiow passage and constructed to maintain a normal mean temperaturetherein higher than the fuel ash fusion temperature, heat absorbingsurface lining the sides of said upfiow passage and constructed tomaintain a normal mean temperature therein lower than the fuel ashfusion temperature, means arranged to form a pervious fiuid cooledscreen between the lower end of said baflle and an intermediate portionof the furnace bottom, a; fioor forming the furnace bottom at the frontside of said screen, and a hopper forming the furnace bottom at the rearside of said screen.

17. In a furnace having a furnace chamber divided into a downfiowpassage and an upfiow passage communicating at their lower ends, themethod of burning finely divided solid fuel and recovering ashconstituents of the fuel in the furnace which comprises introducing astream of finely divided solid fuel into the upper end of and burningthe, fuel in suspension in said downfiow passage, maintaining a normalmean temperature in said downfiow passage above the-fuel ash fusiontemperature, in said downfiow passage will be in a molten condition,molten ash on the portion of the furnace bottom below said downfiowpassage, maintaining a. normal mean temperature in said upfiow passagebelow the fuel ash fusion temperature, whereby ash separating out insaid upfiow passage will be in a dry condition, and collecting ashseparating in said upfiow passage in a portion of the furnace bottombelow said upfiow passage and separate from the bottom portionsupporting the layer of molten ash.

18. In a furnace having a furnace chamber divided into a downfiowpassage and an upfiow passage communicating at their lower ends, themethod of burning finely divided solid fuel and recovering ashconstituents of the fuel in the furnace which comprises introducing astream of, finely divided solid fuel and air for combustion collectingand maintaining a layer of :1

whereby ash separating out into the upper end of and burning the fuel insus/- pension in said downfiow passage, maintaining a normal meantemperature in said downfiow passage above the fuel ash fusiontemperature, out in said downfiow passage will be in a molten condition,collecting and maintaining a layer of molten ash on the portion of thefurnace bottom below said downflow passage, maintaining a normal meantemperature in said upfiow passage below the fuel ash fusiontemperature, whereby ash separating out in said upfiow passage will bein a dry condition, collecting ash separating in said upfiow passage ina portion of the furnace bottom below said upfiow passage and separatefrom the bottom portion supporting the layer of molten ash, andseparately removing the molten and dry ash from the furnace chamber.

ERVIN G. BAILEY. RALPH M. HARDGROVE. HOWARD J. KERR.

